(1) Field of the Invention
This invention relates to automatically guiding a vehicle to follow a discernable path. An example is the automatic guiding of an agricultural harvester along a row of plants.
(2) Description of the Related Art
Guidance systems in existence today use sensors. These sensors, produce a signal variable with the relative position of the vehicle to the desired path. As the vehicle moves in relation to the path, a signal is produced comparable to the linear displacement. Equipment such as a specialized digital computer is used to evaluate this signal and produce a correction signal, resulting in controlling guide wheels to turn right or left. As the guide wheel is turned an additional sensor is used to monitor the guide wheel position and cause a resultant signal to cancel the action originally taken.
While this technique proves to perform the vehicle guidance under most circumstance, certain precision factors are ignored. A device controlled by the operator must be adjusted to determine when the guide wheels are in alignment and parallel to the vehicle axis, the point at which the crop sensor indicates proper alignment, and the exact ratio to guide wheel movement the instrument will equalize.
Also known was a guidance system using digital optical sensors capable of determining angular displacements consistently of 0.33 degrees throughout its life. Each sensor has a "zero" azimuth marker. The sensor measures angular displacement from the zero azimuth, with one direction positive and the other negative.
A digital motor with rotational travel resolution of 1.66 degrees has been used to move the steering wheel as needed from calculations of the computer. The system is fully digital from the input of the sensing system to the output which controls the steering device, therefore precise movement is accomplished consistently.